WASHINGTON  Vice President Cheney will be called to testify in the CIA leak case, lawyers for Cheney's former chief of staff said in court Tuesday.

"We're calling the vice president," said Ted Wells, an attorney for Lewis "Scooter" Libby. Libby is charged with perjury and obstruction in statements he made to prosecutors and grand jurors about what he told reporters about former CIA operative Valerie Plame. Libby has pleaded not guilty.

Plame's identity was leaked to reporters around the same time her husband, former ambassador Joseph Wilson, publicly criticized intelligence used by the White House before the Iraq war.

Cheney's testimony would be historic. Sitting presidents, including Bill Clinton and Gerald Ford, have testified in criminal cases but presidential historians, such as New York University's Paul Light, said they knew of no vice president who has done so.

Cheney and President Bush were questioned during the grand jury phase of the case. As many as two dozen current or former administration officials also were questioned.

Vice President Spiro Agnew resigned in 1973 and pleaded no contest to criminal charges of tax evasion and money laundering. But Agnew never testified, said presidential historian Richard Shenkman, editor of George Mason University's History News Network.

"The question is whether Cheney will argue that his conversations with Libby are confidential and any testimony would impinge on his ability to get honest advice," Light said.

William Jeffress, another of Libby's attorneys, said he did not expect Cheney to resist testifying.

"We've cooperated fully in this matter and will continue to do so in fairness to the parties involved," said Lea Anne McBride, a Cheney spokeswoman. "We're not going to comment further on a legal proceeding."

Neither Jeffress nor Wells would say whether they expect Cheney to testify in court or to give videotaped testimony.

The trial is scheduled to start next month.

In addition to Cheney, other likely witnesses in the trial include former New York Times reporter Judith Miller and NBC News Washington bureau chief Tim Russert.

The leak of Plame's identity in 2003 led to a two-year inquiry by U.S. Attorney Patrick Fitzgerald. Libby is the only person charged in the case.